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IOSTAT(1)                     Linux User's Manual                    IOSTAT(1)



NAME
       iostat  -  Report Central Processing Unit (CPU) statistics and input/output statis-
       tics for devices, partitions and network filesystems (NFS).

SYNOPSIS
       iostat [ -c ] [ -d ] [ -N ] [ -n ] [ -h ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -y ] [
       -z  ]  [  -j  {  ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ] ] [ device
       [...] | ALL ] [ -p [ device [,...] | ALL ] ] [ interval [ count ] ]

DESCRIPTION
       The iostat command is used for monitoring system  input/output  device  loading  by
       observing  the  time  the  devices are active in relation to their average transfer
       rates. The iostat command generates reports that can be used to change system  con-
       figuration to better balance the input/output load between physical disks.

       The first report generated by the iostat command provides statistics concerning the
       time since the system was booted, unless the -y option is  used,  when  this  first
       report  is  omitted.  Each  subsequent  report  covers  the time since the previous
       report. All statistics are reported each time the iostat command is run. The report
       consists of a CPU header row followed by a row of CPU statistics. On multiprocessor
       systems, CPU statistics are calculated system-wide as averages  among  all  proces-
       sors.  A  device  header row is displayed followed by a line of statistics for each
       device that is configured.  When option -n is used, an NFS header row is  displayed
       followed by a line of statistics for each network filesystem that is mounted.

       The interval parameter specifies the amount of time in seconds between each report.
       The first report contains statistics for the  time  since  system  startup  (boot),
       unless  the -y option is used, when this report is omitted.  Each subsequent report
       contains statistics collected during the interval since the  previous  report.  The
       count parameter can be specified in conjunction with the interval parameter. If the
       count parameter is specified, the value of count determines the number  of  reports
       generated at interval seconds apart. If the interval parameter is specified without
       the count parameter, the iostat command generates reports continuously.


REPORTS
       The iostat command generates three types of reports, the  CPU  Utilization  report,
       the Device Utilization report and the Network Filesystem report.

       CPU Utilization Report
              The  first  report  generated  by  the iostat command is the CPU Utilization
              Report. For multiprocessor systems, the CPU values are global averages among
              all processors.  The report has the following format:

              %user
                     Show  the percentage of CPU utilization that occurred while executing
                     at the user level (application).

              %nice
                     Show the percentage of CPU utilization that occurred while  executing
                     at the user level with nice priority.

              %system
                     Show  the percentage of CPU utilization that occurred while executing
                     at the system level (kernel).

              %iowait
                     Show the percentage of time that the CPU or  CPUs  were  idle  during
                     which the system had an outstanding disk I/O request.

              %steal
                     Show  the percentage of time spent in involuntary wait by the virtual
                     CPU or CPUs while the hypervisor was servicing another  virtual  pro-
                     cessor.

              %idle
                     Show  the  percentage  of time that the CPU or CPUs were idle and the
                     system did not have an outstanding disk I/O request.

       Device Utilization Report
              The second report generated by the iostat command is the Device  Utilization
              Report.  The  device  report provides statistics on a per physical device or
              partition basis. Block devices for which statistics are to be displayed  may
              be  entered  on the command line. Partitions may also be entered on the com-
              mand line providing that option -x is not used.  If no device nor  partition
              is  entered, then statistics are displayed for every device used by the sys-
              tem, and providing that the kernel maintains statistics for it.  If the  ALL
              keyword  is  given  on  the  command line, then statistics are displayed for
              every device defined by the system, including those  that  have  never  been
              used.   The  report  may  show  the following fields, depending on the flags
              used:

              Device:
                     This column gives the device (or partition) name, which is  displayed
                     as  hdiskn  with  2.2 kernels, for the nth device. It is displayed as
                     devm-n with 2.4 kernels, where m is the major number of  the  device,
                     and  n  a distinctive number.  With newer kernels, the device name as
                     listed in the /dev directory is displayed.

              tps
                     Indicate the number of transfers per second that were issued  to  the
                     device.  A transfer is an I/O request to the device. Multiple logical
                     requests can be combined into a single I/O request to the  device.  A
                     transfer is of indeterminate size.

              Blk_read/s
                     Indicate  the amount of data read from the device expressed in a num-
                     ber of blocks per second. Blocks are equivalent to sectors with  ker-
                     nels 2.4 and later and therefore have a size of 512 bytes. With older
                     kernels, a block is of indeterminate size.

              Blk_wrtn/s
                     Indicate the amount of data written to the device expressed in a num-
                     ber of blocks per second.

              Blk_read
                     The total number of blocks read.

              Blk_wrtn
                     The total number of blocks written.

              kB_read/s
                     Indicate  the  amount of data read from the device expressed in kilo-
                     bytes per second.

              kB_wrtn/s
                     Indicate the amount of data written to the device expressed in  kilo-
                     bytes per second.

              kB_read
                     The total number of kilobytes read.

              kB_wrtn
                     The total number of kilobytes written.

              MB_read/s
                     Indicate  the  amount  of  data  read  from  the  device expressed in
                     megabytes per second.

              MB_wrtn/s
                     Indicate the amount of  data  written  to  the  device  expressed  in
                     megabytes per second.

              MB_read
                     The total number of megabytes read.

              MB_wrtn
                     The total number of megabytes written.

              rrqm/s
                     The number of read requests merged per second that were queued to the
                     device.

              wrqm/s
                     The number of write requests merged per second that  were  queued  to
                     the device.

              r/s
                     The  number  of read requests that were issued to the device per sec-
                     ond.

              w/s
                     The number of write requests that were issued to the device per  sec-
                     ond.

              rsec/s
                     The number of sectors read from the device per second.

              wsec/s
                     The number of sectors written to the device per second.

              rkB/s
                     The number of kilobytes read from the device per second.

              wkB/s
                     The number of kilobytes written to the device per second.

              rMB/s
                     The number of megabytes read from the device per second.

              wMB/s
                     The number of megabytes written to the device per second.

              avgrq-sz
                     The average size (in sectors) of the requests that were issued to the
                     device.

              avgqu-sz
                     The average queue length of the requests  that  were  issued  to  the
                     device.

              await
                     The  average  time  (in  milliseconds) for I/O requests issued to the
                     device to be served. This includes the time spent by the requests  in
                     queue and the time spent servicing them.

              svctm
                     The average service time (in milliseconds) for I/O requests that were
                     issued to the device. Warning! Do not trust this field any more. This
                     field will be removed in a future sysstat version.

              %util
                     Percentage  of  elapsed time during which I/O requests were issued to
                     the device (bandwidth utilization for the device). Device  saturation
                     occurs when this value is close to 100%.

       Network Filesystem report
              The  Network  Filesystem  (NFS)  report provides statistics for each mounted
              network filesystem.  The report shows the following fields:

              Filesystem:
                     This columns shows the hostname of the NFS server followed by a colon
                     and by the directory name where the network filesystem is mounted.

              rBlk_nor/s
                     Indicate  the  number  of blocks read by applications via the read(2)
                     system call interface. A block has a size of 512 bytes.

              wBlk_nor/s
                     Indicate the  number  of  blocks  written  by  applications  via  the
                     write(2) system call interface.

              rBlk_dir/s
                     Indicate  the  number  of  blocks  read  from  files  opened with the
                     O_DIRECT flag.

              wBlk_dir/s
                     Indicate the number of  blocks  written  to  files  opened  with  the
                     O_DIRECT flag.

              rBlk_svr/s
                     Indicate  the number of blocks read from the server by the NFS client
                     via an NFS READ request.

              wBlk_svr/s
                     Indicate the number of blocks written to the server by the NFS client
                     via an NFS WRITE request.

              rkB_nor/s
                     Indicate the number of kilobytes read by applications via the read(2)
                     system call interface.

              wkB_nor/s
                     Indicate the number of kilobytes  written  by  applications  via  the
                     write(2) system call interface.

              rkB_dir/s
                     Indicate  the  number  of  kilobytes  read from files opened with the
                     O_DIRECT flag.

              wkB_dir/s
                     Indicate the number of kilobytes written to  files  opened  with  the
                     O_DIRECT flag.

              rkB_svr/s
                     Indicate  the  number  of  kilobytes  read from the server by the NFS
                     client via an NFS READ request.

              wkB_svr/s
                     Indicate the number of kilobytes written to the  server  by  the  NFS
                     client via an NFS WRITE request.

              rMB_nor/s
                     Indicate the number of megabytes read by applications via the read(2)
                     system call interface.

              wMB_nor/s
                     Indicate the number of megabytes  written  by  applications  via  the
                     write(2) system call interface.

              rMB_dir/s
                     Indicate  the  number  of  megabytes  read from files opened with the
                     O_DIRECT flag.

              wMB_dir/s
                     Indicate the number of megabytes written to  files  opened  with  the
                     O_DIRECT flag.

              rMB_svr/s
                     Indicate  the  number  of  megabytes  read from the server by the NFS
                     client via an NFS READ request.

              wMB_svr/s
                     Indicate the number of megabytes written to the  server  by  the  NFS
                     client via an NFS WRITE request.

              ops/s
                     Indicate  the number of operations that were issued to the filesystem
                     per second.

              rops/s
                     Indicate the number of 'read' operations  that  were  issued  to  the
                     filesystem per second.

              wops/s
                     Indicate  the  number  of  'write' operations that were issued to the
                     filesystem per second.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -h     Make the NFS report displayed by option -n easier to read by a human.

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display persistent device names. Options ID, LABEL, etc. specify the type of
              the  persistent  name.  These  options are not limited, only prerequisite is
              that directory with required  persistent  names  is  present  in  /dev/disk.
              Optionally,  multiple devices can be specified in the chosen persistent name
              type.

       -k     Display statistics in kilobytes per second instead  of  blocks  per  second.
              Data displayed are valid only with kernels 2.4 and later.

       -m     Display  statistics  in  megabytes per second instead of blocks or kilobytes
              per second.  Data displayed are valid only with kernels 2.4 and later.

       -N     Display the registered device mapper names for any  device  mapper  devices.
              Useful for viewing LVM2 statistics.

       -n     Display  the  network  filesystem  (NFS) report. This option works only with
              kernel 2.6.17 and later.

       -p [ { device [,...] | ALL } ]
              The -p option displays statistics for block devices and all their partitions
              that  are  used  by  the system.  If a device name is entered on the command
              line, then statistics for it and all its partitions are displayed. Last, the
              ALL keyword indicates that statistics have to be displayed for all the block
              devices and partitions defined by the  system,  including  those  that  have
              never been used. If option -j is defined before this option, devices entered
              on the command line can be specified with the chosen persistent  name  type.
              Note that this option works only with post 2.5 kernels.

       -t     Print the time for each report displayed. The timestamp format may depend on
              the value of the S_TIME_FORMAT environment variable (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.  This option works with post 2.5 kernels  since
              it needs /proc/diskstats file or a mounted sysfs to get the statistics. This
              option may also work with older kernels (e.g. 2.4) only if extended  statis-
              tics  are  available in /proc/partitions (the kernel needs to be patched for
              that).

       -y     Omit first report with statistics since the system boot, if displaying  mul-
              tiple records in given interval.

       -z     Tell  iostat  to omit output for any devices for which there was no activity
              during the sample period.


ENVIRONMENT
       The iostat command takes into account the following environment variable:


       S_TIME_FORMAT
              If this variable exists and its value is ISO then the current locale will be
              ignored when printing the date in the report header. The iostat command will
              use the ISO 8601 format (YYYY-MM-DD) instead.  The timestamp displayed  with
              option -t will also be compliant with ISO 8601 format.


EXAMPLES
       iostat
              Display a single history since boot report for all CPU and Devices.

       iostat -d 2
              Display a continuous device report at two second intervals.

       iostat -d 2 6
              Display six reports at two second intervals for all devices.

       iostat -x hda hdb 2 6
              Display  six  reports  of  extended  statistics  at two second intervals for
              devices hda and hdb.

       iostat -p sda 2 6
              Display six reports at two second intervals for device sda and all its  par-
              titions (sda1, etc.)

BUGS
       /proc filesystem must be mounted for iostat to work.

       Extended statistics are available only with post 2.5 kernels.

       The  average service time (svctm field) value is meaningless, as I/O statistics are
       calculated at block level, and we don't know when the disk driver starts to process
       a request. For this reason, this field will be removed in a future sysstat version.


FILES
       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

       /proc/partitions contains disk statistics (for  pre  2.5  kernels  that  have  been
       patched).

       /proc/diskstats contains disks statistics (for post 2.5 kernels).

       /sys contains statistics for block devices (post 2.5 kernels).

       /proc/self/mountstats contains statistics for network filesystems.

       /dev/disk contains persistent device names.

AUTHOR
       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO
       sar(1), pidstat(1), mpstat(1), vmstat(8)

       http://pagesperso-orange.fr/sebastien.godard/



Linux                             APRIL 2009                         IOSTAT(1)

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